The present invention relates to a method for maintenance of a transportation device, a software program, and a controller.
There are many kinds of transportation devices using an electric motor for propelling, e.g. elevators, escalators, speedways, cable cars, railways, etc. The background of the invention will be described for an elevator, but may be applied to other transportation devices as well. In an elevator, the accurate elevator position is needed to fulfill functionality and performance requirements of the elevator. Typically there is an incremental encoder attached either directly to the shaft or to the surface via wheel of an electrical motor moving the elevator car. Rotor angular speed and elevator position is calculated from the encoder pulses based on received pulses and information about encoder properties. One such encoder property is a parameter called Pulses Per Revolution (PPR), which defines how many encoder pulses are received during one revolution of the rotor. There are many fault modes related to this measurement including but not limited to:                Electrical disturbances deteriorate pulse waveforms and lead to missing/additional pulse,        Wrong configuration (e.g. wrong pulse number like 8000 PPR instead of correct 8192 PPR),        Slipping wheel at the rotor surface due to too little friction or worn/damaged wheel material.        
These failures may lead to wrong speed measurement and elevator position, leading to problems in the elevator system. When the failure effects are severe, some control system may detect them already and creates an error code. However, it is difficult to identify a possible failure at an early stage where effects are not such severe.
When controlling a Permanent Magnet Synchronous Motor (PMSM) with closed loop control, it is essential to get proper rotor orientation. It is known that the control may provide a good estimate about electrical supply frequency of the motor and thus the orientation.